Isopiestic balance

In the ORNL s isopiestic system (Holmes et al., 1978 Holmes and Mesmer, 1986), operating at temperatures and pressures up to 250 °C and 3.5 MPa, a number of electrolyte solutions, placed in different metallic cups, attain an equilibrium with a common vapor phase at a well-controlled temperature. The equilibrium compositions are determined by weighing the cups in place (inside of the pressure vessel) with an electromagnetic balance calibrated frequently using a set of standard masses interspersed with the solution cups (Figure 1.7). 

Isopiestic vapor sorption can be made using an electronic microhalance instead of the quartz spring balance. Electronic microbalances are commercially available from a number of producers. Their main advantages are their high resolution and their ability to allow kinetic measurements. Additionally, experiments using electronic microbalances can be automated easily and provide computing facilities. 

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